Heat exchanger and process for fabricating same

ABSTRACT

A heat exchanger for use as an evaporator, for example, in refrigerators wherein a hydrocarbon refrigerant is used. The heat exchanger comprises a finned zigzag tube  1  comprising a zigzag tube member  2  formed by bending a pipe having no welded seams, the zigzag tube member  2  having at least three straight tube portions  2   a  arranged from the front rearward at a spacing and parallel to one another, a plurality of first fin groups  3  arranged at a spacing on two adjacent straight tube portions  2   a  of the zigzag tube member  2  longitudinally of the straight tube portions and each comprising plate fins  5  extending across and fixedly arranged in parallel on the adjacent straight tube portions  2   a , and a plurality of second fin groups  4  each comprising plate fins  6  fixedly arranged in parallel on each remaining straight tube portion  2   a  of the zigzag tube member  2 , the second fin groups  4  being arranged at a spacing on the remaining straight tube portion  2   a  longitudinally thereof so as to be in the same positions as the respective first fin groups  3  with respect to the longitudinally direction of the straight tube portions  2   a . The heat exchanger E comprising the finned zigzag tube  1  exhibits the desired refrigeration performance with the leakage of refrigerant diminished.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is an application filed under 35 U.S.C. §111(a)claiming the benefit pursuant to 35 U.S.C. §119(e)(1) of the filing dateof Provisional Application No. 60/356,117 filed Feb. 14, 2002 pursuantto 35 U.S.C. §111(b).

TECHNICAL FIELD

The present invention relates to heat exchangers, for example, for useas evaporators in refrigeration devices such as refrigerators orrefrigerated showcases, and to a process for fabricating the heatexchanger.

The direction indicated by the arrow X in FIGS. 3 and 7 will be referredto as “front,” and the opposite direction as “rear.” FIGS. 1, 4 and 5are also based on the same front-rear relation. The upper and lowersides of the drawings will be referred to as “upper” and “lower,”respectively, and the left- and right-hand sides of FIGS. 1, 3, 4 and 7as “left” and “right,” respectively.

BACKGROUND ART

FIG. 7 shows an evaporator conventionally used in refrigeration devicessuch as refrigerators or refrigerated showcases. With reference to FIG.7, the conventional evaporator 30 comprises two fin groups 32 arrangedone above the other at a spacing and each comprising a plurality ofplate fins 31 arranged in parallel from left to right, a plurality ofstraight tubes 33 arranged at a spacing from the front rearward andextending through all the plate fins 31 of the upper and lower fingroups 32, and a plurality of bends 34 interconnecting the respectivepairs of adjacent straight tubs 33 so as to pass a refrigerant throughall the straight tubes 33 one after another.

The evaporator 30 is fabricated by the following process. First preparedare a plurality of straight tubes 33, plate fins 31 each having holes,and a tube enlarging device comprising a wire and a tube enlarging ballattached to one end of the wire. All the straight tubes 33 are theninserted through the respective holes of each plate fin 31. The wire ofthe tube enlarging device is thereafter inserted through each tube fromone end thereof and pulled at the other end to force the ball throughthe tube 33 to enlarge the tube 33 and fixedly fit all the plate fins 31around the tube. The ends of the straight tubes 33 are then welded toopposite ends of U-shaped bends 34 to thereby interconnect all thestraight tubes 33 by the bends 34. In this way, the evaporator 30 isfabricated.

Studies are recently under way for the use of hydrocarbon refrigerantswhich are less likely to destroy the ozone layer and to influence globalwarming, in refrigerators, refrigerated showcases and like refrigerationdevices as substitutes for chlorofluorocarbon refrigerants. Since thehydrocarbon refrigerants are flammable, there is a need to minimize theleakage of the refrigerant.

With the conventional evaporator 30 described above, however, thestraight tubes 33 are welded to the U-shaped bends 34, so that therefrigerant is likely to leak from the welded joints.

Accordingly, it is thought that this problem can be overcome by anevaporator prepared from a finned hairpin tube which comprises a hairpintube, and a plurality of fin groups arranged on the hairpin tubelongitudinally thereof at a spacing and each comprising parallel platefins extending across and fixed to the two straight tube portions of thehairpin tube, by bending the finned hairpin tube zigzag in its entiretyat portions thereof having no fin groups.

This evaporator is fabricated by the process to be described below.First prepared are a hairpin tube, a multiplicity of plate fins eachhaving two holes which are spaced apart, and a tube enlarging devicecomprising a pressure rod and an enlarging mandrel attached to one endof the rod. The two straight tube portions of the hairpin tube are theninserted through the respective holes of each plate fin to therebyarrange the plate fins in parallel into a plurality of unfixed fingroups as spaced apart on the tube portions longitudinally thereof. Themandrel of the tube enlarging device is subsequently forced into thestraight tube portions from each open end of the hairpin tube to enlargethe tube portions and to fixedly fit the plate fins of each fin grouparound the tube portions of the hairpin tube, whereby a finned hairpintube is produced. The finned hairpin tube is thereafter bent into azigzag form in its entirety at portions thereof having no fin groups. Inthis way, the evaporator is fabricated.

The evaporator fabricated by this process has no joints formed in thehairpin tube of the finned hairpin tube, so that no leakage of therefrigerant occurs unlike the evaporator 30 shown in FIG. 7. However,the evaporator is less effective for achieving an improved refrigerationefficiency by an increase in heat transfer area since the plate fins aremerely so sized as to extend across the two straight tube portions.

An object of the present invention is to overcome the foregoing problemsand to provide a heat exchanger which is capable of exhibiting thedesired refrigeration performance with the leakage of refrigerantdiminished when used as an evaporator in refrigeration devices.

DISCLOSURE OF THE INVENTION

The present invention provides a heat exchanger comprising a zigzag tubeformed by bending a pipe having no welded seams and having at leastthree straight tube portions arranged from the front rearward at aspacing and parallel to one another, and a plurality of plate finsfixedly fitted around the straight tube portions.

With the heat exchanger of the invention, the zigzag tube is prepared bybending a single pipe having no welded seams, so that the heat exchangeris usable free from the leakage of refrigerant as an evaporator inrefrigeration devices. The heat exchanger is therefore adapted for usewith a hydrocarbon refrigerant which is less likely to destroy the ozonelayer and to influence global warming. Since the heat exchangercomprises a zigzag tube having at least three straight tube portionsarranged in parallel to one another, and plate fins fixedly fittedaround the straight tube portions, an increased number of plate fins canbe provided in the exchanger to give an increased heat transfer area andachieve an improved heat exchange efficiency, e.g., an improvedrefrigeration efficiency when the exchanger is used as the evaporator ofthe refrigeration device.

The heat exchanger of the invention may comprise a first fin groupcomprising a plurality of plate fins extending across and fixedlyarranged in parallel on two adjacent straight tube portions of thezigzag tube, and a second fin group comprising a plurality of plate finsfixedly arranged in parallel on each remaining straight tube portion ofthe zigzag tube. This provides an increased number of fin plates in theheat exchanger, giving an increased heat transfer area to achieve animproved heat exchange efficiency, e.g., an improved refrigerationefficiency when the exchanger is used as an evaporator in refrigerationdevices.

With the heat exchanger of the invention, the zigzag tube may beintegrally provided on an inner peripheral surface thereof with innerfins extending longitudinally thereof and arranged at a spacingcircumferentially thereof. The heat exchanger then exhibits improvedheat exchange performance.

Each plate fin of the heat exchanger of the invention may be fixed tothe straight tube portion of the zigzag tube by enlarging the tube withuse of a fluid. Even if the zigzag tube in this case has inner finsprojecting from the inner peripheral surface thereof to a relativelygreat height in order to afford an increased heat transfer area, thedesired refrigeration performance (heat exchange performance) isavailable without the likelihood of the tube enlargement collapsing theinner fin.

With the heat exchanger of the invention, the zigzag tube may have highand low two kinds of inner fins alternately arranged circumferentiallythereof and projecting from the inner peripheral surface of the tube todifferent heights, the high inner fins being 0.7 to 1.7 mm in heightfrom the tube surface, the low inner fins being 0.4 to 1.2 mm in heightfrom the surface. The heat exchanger then effectively improved in heatexchange performance.

With the heat exchanger of the invention wherein the zigzag tube has thehigh and low two kinds of inner fins, the pitch of the inner fins is 0.4to 1.6 mm.

With the heat exchanger of the invention wherein the zigzag tube has thehigh and low two kinds of inner fins, the zigzag tube is 6 to 10 mm inoutside diameter and 0.4 to 0.8 mm in the wall thickness of acircumferential wall thereof.

With the heat exchanger of the invention, all the inner fins are equalin height and are 0.7 to 1.2 mm in height from the inner peripheralsurface of the zigzag tube. The heat exchanger then exhibits stillimproved heat exchange performance.

With the heat exchanger of the invention wherein all the inner fins areequal in height, the pitch of the inner fins may be 0.4 to 1.6 mm.

With the heat exchanger of the invention wherein all the inner fins areequal in height, the zigzag tube may be 6 to 10 mm in outside diameterand 0.4 to 0.8 mm in the wall thickness of a circumferential wallthereof.

With the heat exchanger of the invention, the front-to-rear length ofthe plate fins of the second fin group is approximately one half thefront-to-rear length of the plate fins of the first fin group.

With the heat exchanger of the invention, the first fin group may bedifferent from the second fin group in fin pitch. For example, thesecond fin group is greater than the first fin group in fin pitch.

The present invention provides another heat exchanger comprising afinned zigzag tube including a zigzag tube member formed by bending apipe having no welded seams, the zigzag tube member having at leastthree straight tube portions arranged from the front rearward at aspacing and parallel to one another, a plurality of first fin groupsarranged at a spacing on two adjacent straight tube portions of thezigzag tube member longitudinally of the straight tube portions and eachcomprising a plurality of plate fins extending across and fixedlyarranged in parallel on the adjacent straight tube portions, and aplurality of second fin groups each comprising a plurality of plate finsfixedly arranged in parallel on each remaining straight tube portion ofthe zigzag tube member, the second fin groups being arranged at aspacing on the remaining straight tube portion longitudinally thereof soas to be in the same positions as the respective first fin groups withrespect to the longitudinally direction of the straight tube portions,the finned zigzag tube being bent between the first fin groups andbetween the second fin groups on all the straight tube portions so as toposition the first fin groups one above another and the second fingroups one above another in superposed layers, the spacing between theadjacent first fin groups and the spacing between the second fin groupsbeing a length permitting bending of the straight tube portions of thefinned zigzag tube.

With the second-mentioned heat exchanger of the invention, the zigzagtube is prepared by bending a single pipe having no welded seams, sothat the heat exchanger is usable free from the leakage of refrigerantas an evaporator in refrigeration devices. The heat exchanger istherefore adapted for use with a hydrocarbon refrigerant which is lesslikely to destroy the ozone layer and to influence global warming. Sincethe heat exchanger comprises first fin groups each comprising aplurality of plate fins extending across and fixedly arranged inparallel on two adjacent straight tube portions of the zigzag tubemember, and second fin groups each comprising plate fins fixedlyarranged in parallel on each remaining straight tube portion of thezigzag tube member, an increased number of plate fins can be provided inthe exchanger to give an increased heat transfer area and achieve animproved heat exchange efficiency, e.g., an improved refrigerationefficiency when the exchanger is used as the evaporator of therefrigeration device. Especially because the first fin groups, as wellas the second fin groups, are arranged in at least two superposedstages, this arrangement affords an increased heat transfer area toachieve a further improved heat exchange efficiency, e.g., a greatlyimproved refrigeration efficiency when the exchanger is used as theevaporator of the refrigeration device.

With the second-mentioned heat exchanger of the invention, the zigzagtube member may be integrally provided on an inner peripheral surfacethereof with inner fins extending longitudinally thereof and arranged ata spacing circumferentially thereof. The heat exchanger then exhibitsimproved heat exchange performance.

Each plate fin of the second-mentioned heat exchanger of the inventionmay be fixed to the straight tube portion of the zigzag tube member byenlarging the tube member with use of a fluid. Even if the zigzag tubemember in this case has inner fins projecting from the inner peripheralsurface thereof to a relatively great height in order to afford anincreased heat transfer area, the desired refrigeration performance(heat exchange performance) is available without the likelihood of thetube member enlargement collapsing the inner fin.

With the second-mentioned heat exchanger of the invention, the zigzagtube member may have high and low two kinds of inner fins alternatelyarranged circumferentially thereof and projecting from the innerperipheral surface of the tube member to different heights, the highinner fins being 0.7 to 1.7 mm in height from the tube member surface,the low inner fins being 0.4 to 1.2 mm in height from the surface. Theheat exchanger then effectively improved in heat exchange performance.

With the second-mentioned heat exchanger of the invention wherein thezigzag tube member has the high and low two kinds of inner fins on theinner peripheral surface thereof, the pitch of the inner fins is 0.4 to1.6 mm.

With the second-mentioned heat exchanger of the invention wherein thezigzag tube member has the high and low two kinds of inner fins on theinner peripheral surface thereof, the zigzag tube member is 6 to 10 mmin outside diameter and 0.4 to 0.8 mm in the wall thickness of acircumferential wall thereof.

With the second-mentioned heat exchanger of the invention, all the innerfins are equal in height and are 0.7 to 1.2 mm in height from the innerperipheral surface of the zigzag tube member. The heat exchanger thenexhibits still improved heat exchange performance.

With the second-mentioned heat exchanger of the invention wherein allthe inner fins are equal in height, the pitch of the inner fins may be0.4 to 1.6 mm.

With the second-mentioned heat exchanger of the invention wherein allthe inner fins are equal in height, the zigzag tube member may be 6 to10 mm in outside diameter and 0.4 to 0.8 mm in the wall thickness of acircumferential wall thereof.

With the second-mentioned heat exchanger of the invention, thefront-to-rear length of the plate fins of the second fin groups isapproximately one half the front-to-rear length of the plate fins of thefirst fin groups.

With the second-mentioned heat exchanger of the invention, the first fingroups may be different from the second fin groups in fin pitch. Forexample, the second fin groups are greater than the first fin groups infin pitch.

The present invention provides a refrigeration device which has arefrigeration cycle having a compressor, a condenser and an evaporator,the evaporator being one of the heat exchangers described wherein ahydrocarbon refrigerant is used as the refrigerant and circulated at arate of 1 to 9 kg/h.

The present invention provides a process for fabricating a heatexchanger, i.e., a heat exchanger according to claim 2, which processincludes preparing a hairpin tube by bending a pipe having no weldedseams and a multiplicity of plate fins each having two holes spacedapart in a forward or rearward direction, inserting two straight tubeportions of the hairpin tube through the respective holes of all theplate fins to thereby arrange the plate fins in parallel into apredetermined number of unfixed fin groups spaced apart on the straighttube portions longitudinally thereof by a length permitting bending ofthe straight tube portions; enlarging the hairpin tube to fixedlyposition the plate fins across the two straight tube portions to obtaina finned hairpin tube having a dividable fin group for forming secondfin groups and a first fin group; dividing the plate fins of the entiredividable fin group into portions fixed to one of the straight tubeportions and portions fixed to the other straight tube portion to formthe second fin groups and outwardly bending the two straight tubeportions of the finned hairpin tube forward and rearward respectively.

The heat exchanger according to claim 2 and having the foregoingadvantage can be fabricated by this process of the invention relativelyeasily.

The present invention provides a process for fabricating another heatexchanger, i.e. a heat exchanger according to claim 14, which processincludes preparing a hairpin tube by bending a pipe having no weldedseams and a multiplicity of plate fins each having two holes spacedapart in a forward or rearward direction, inserting two straight tubeportions of the hairpin tube through the respective holes of all theplate fins to thereby arrange the plate fins in parallel into apredetermined number of unfixed fin groups spaced apart on the straighttube portions longitudinally thereof by a length permitting bending ofthe straight tube portions; the predetermined number being n (which isan integer of not smaller than 2) times the number, not smaller than 2,of unfixed fin groups positioned closer to a bent portion of the hairpintube for forming first fin groups; enlarging the hairpin tube to fixedlyposition the plate fins across the two straight tube portions to obtaina finned hairpin tube having dividable fin groups for forming second fingroups and the first fin group; dividing the plate fins of all thedividable fin groups into portions fixed to one of the straight tubeportions and portions fixed to the other straight tube portion to formthe second fin groups and outwardly bending the two straight tubeportions of the finned hairpin tube forward and rearward respectively.

The heat exchanger according to claim 14 and having the foregoingadvantage can be fabricated by the second-mentioned process of theinvention relatively easily.

In the process of the invention for fabricating either one of the twoheat exchangers, the hairpin tube may be integrally provided on an innerperipheral surface thereof with inner fins extending longitudinallythereof and arranged at a spacing circumferentially thereof.

In the process of the invention for fabricating either one of the twoheat exchangers, the hairpin tube may be enlarged with use of a fluid.

In the process of the invention for fabricating either one of the twoheat exchangers, the hairpin tube may have high and low two kinds ofinner fins alternately arranged circumferentially thereof and projectingfrom the inner peripheral surface of the tube to different heights, thehigh inner fins being 0.7 to 1.7 mm in height from the tube surface, thelow inner fins being 0.4 to 1.2 mm in height from the surface.

In the process of the invention for fabricating either one of the twoheat exchangers wherein the hairpin tube has the high and low two kindsof inner fins on the inner peripheral surface thereof, the pitch of theinner fins is 0.4 to 1.6 mm.

In the process of the invention for fabricating either one of the twoheat exchangers wherein the hairpin tube has the high and low two kindsof inner fins on the inner peripheral surface thereof, the hairpin tubeis 6 to 10 mm in outside diameter and 0.4 to 0.8 mm in the wallthickness of a circumferential wall thereof.

In the process of the invention for fabricating either one of the twoheat exchangers, all the inner fins are equal in height and are 0.7 to1.2 mm in height from the inner peripheral surface of the hairpin tube.

In the process of the invention for fabricating either one of the twoheat exchangers wherein all the inner fins are equal in height, thepitch of the inner fins may be 0.4 to 1.6 mm.

In the process of the invention for fabricating either one of the twoheat exchangers wherein all the inner fins are equal in height, thehairpin tube may be 6 to 10 mm in outside diameter and 0.4 to 0.8 mm inthe wall thickness of a circumferential wall thereof.

In the process of the invention for fabricating either one of the twoheat exchangers, the plate fins of the dividable fin group for formingthe second fin groups may each comprise two fin forming portions andconnecting portions dividably joining the two fin forming portions. Thehairpin tube can then be inserted through the holes of the plate finswith greater ease, and the plate fins are dividable easily in thesubsequent step.

In the process of the invention for fabricating either one of the twoheat exchangers, the plate fins of the first fin group and the platefins of the dividable fin group for forming the second fin groups may beidentical in shape, and the plate fins of the dividable fin group mayeach have a V-shaped notch formed in a midportion of at least one ofupper and lower edges thereof in the forward or rearward direction, anda slit extending upward or downward and formed at the same position asthe notch with respect to the forward or rearward direction, asseparated from the notch. The slitted plate fins can be formed byblanking with use of a die which is used for blanking out the otherplate fins and which is removably provided with a notch forming portionand a slit forming portion. Thus, one type of blanking die is usable forforming two kinds of plate fins, which are therefore made available atreduced costs. Further since the slitted plate fins have a V-shapednotch in the midportion of at least one of upper and lower edges thereofin the forward or rearward direction, and a slit extending upward ordownward and formed at the same position as the notch with respect tothe forward or rearward direction, as separated from the notch canbe-divided easily.

In the process of the invention for fabricating either one of the twoheat exchangers, a straight tube portion having a predetermined numberof second fin groups may be cut off from the finned hairpin tube afterthe second fin groups are formed by dividing the dividable fin group.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a finned zigzag tube forfabricating an evaporator embodying the invention.

FIG. 2 is an enlarged view in section taken along the line II-II in FIG.1.

FIG. 3 is a perspective view showing the evaporator embodying theinvention.

FIG. 4 is a perspective view showing a finned hairpin tube for makingthe finned zigzag tube.

FIG. 5 includes front views showing two kinds of plate fins.

FIG. 6 is a sectional view corresponding to FIG. 2 and showing anotherexample of finned zigzag tube.

FIG. 7 is a perspective view showing a conventional evaporator.

BEST MODE OF CARRYING OUT THE INVENTION

An embodiment of the invention will be described below with reference tothe drawings. The embodiment is a heat exchanger to which the inventionis applied and which is an evaporator for use in refrigeration devices.In the following description, the term “aluminum” includes aluminumalloys in addition to pure aluminum.

FIG. 1 shows a finned zigzag tube 1 which comprises a zigzag tube 2 ofaluminum having at least three, i.e. in this case, four, straight tubeportions 2 a arranged from the front rearward at a spacing, a pluralityof, i.e. in this case, two, first fin groups 3 arranged at a spacing onthe two adjacent straight tube portions 2 a in the center of the zigzagtube 2 longitudinally of the portions 2 a, and a plurality of, i.e. inthis case, two, second fin groups 4 arranged at a spacing on therespective straight tube portions 2 a at the front and rear ends of thezigzag tube 2 longitudinally of the portions 2 a. The spacing betweenthe two first fin groups 3 and the spacing between the two second fingroups 4 are a length permitting the straight tube portions 2 a to be sobent as to position the first fin groups 3 one above the other and thesecond fin groups 4 one above the other in superposed layers.

The zigzag tube 2 is formed by bending a pipe having no welded seams.The tube 2 is integrally provided with high and low two kinds of innerfins 20, 21 projecting from the inner peripheral surface of the tube todifferent heights, extending longitudinally thereof, and alternatelyarranged circumferentially thereof at a spacing. The inner fins 20, 21project toward the center of the zigzag tube 2. The high inner fins 20are 0.7 to 1.7 mm in height h1 as measured from the inner peripheralsurface of the zigzag tube 2, and the low inner fins 21 are 0.4 to 1.2mm in height h2 as measured from the surface of the zigzag tube 2. Thepitch p of the inner fins 20, 21 is 0.4 to 1.6 mm. The pitch p of theinner fins 20, 21 is the circumferential distance, as measured in crosssection on the outer periphery of the zigzag tube 2, between twostraight lines connecting the center line of the zigzag tube 2 and thecenters of the thicknesses of a pair of adjacent inner fins 20, 21. Thezigzag tube 2 is 6 to 10 mm in outside diameter, and 0.4 to 0.8 mm inthe thickness of the circumferential wall thereof.

The first fin group 3 comprises parallel aluminum plate fins 5 extendingacross and fixed to the two straight tube portions 2 a. The plate fins 5are rectangular and elongated in the forward or rearward direction. Theplate fins 5 constituting the first fin group 3 will hereinafter bereferred to as the “first plate fins. The second fin group 4 comprisesaluminum plate fins 6 fixed to the corresponding straight tube portion 2a and is disposed in the same position as the first fin group 3 withrespect to the longitudinal direction of the straight tube portion 2 a.The front-to-rear length of the plate fins 6 of the second fin group 4is equal to one half of the front-to-rear length of the first plate fins5, or is shorter than one half thereof by an amount correspond to thenotch 12 and slit 13 to be described later. The plate fins 6constituting the second fin group 4 will hereinafter be referred to asthe “second plate fins.” The first fin group 3 and the second fin group4 are not always the same in fin pitch; preferably, the second fin group4 is greater than the first fin group 3 in fin pitch.

The first plate fins 5 each have two holes 5 a spaced apart in theforward or rearward direction. The two straight tube portions 2 a in thecenter of the zigzag tube 2 are inserted through the respective holes 5a of all the first plate fins 5, which are fixedly fitted around the twostraight tube portions 2 a by enlarging these tube portions 2 a. Thesecond plate fins 6 each have one hole, and the straight tube portion 2a at the front or rear end of the zigzag tube 2 is inserted through theholes of all the corresponding second plate fins 6, which are fixedlyfitted around the straight tube portion 2 a by enlarging the tubeportion 2 a. Incidentally, the finned zigzag tube 1 is also usable as itis as an evaporator.

As shown in FIG. 3, the finned zigzag tube 1 is bent at a locationbetween the adjacent first fin groups 3 and between the second fingroups 4 where all the straight tube portions 2 a are adjacent to oneanother, so as to position the first fin groups 3 one above the otherand the second fin groups 4 one above the other in superposed layers,whereby an evaporator E is fabricated. This evaporator E has two firstfin groups 3 arranged one above the other in superposed layers, twosecond fin groups 4 arranged one above the other in superposed layers oneach of front and rear sides of these first fin groups 3, front and reartwo straight tube portions 2 b extending through the first plate fins 5of each first fin group 3, and one straight tube portion 2 b extendingthrough the second plate fins 6 of each second fin group 4. At the leftof the fin groups 3, 4, the upper and lower straight tube portions 2 bwhich are in the same position with respect to the forward or rearwarddirection are interconnected by a bent portion 2 c integral with thesetube portions 2 b. Further at the right of the fin groups 3, 4, the twoat each of the front and rear sides of the upper straight tube portions2 b are interconnected by a bent portion 2 d integral with the two, andthe central two of the lower straight tube portions 2 b areinterconnected by a bent portion 2 e integral therewith.

The evaporator will be fabricated by the process to be described below.

First, a finned hairpin tube H shown in FIG. 4 is fabricated.

Prepared for this tube are a hairpin tube 10 formed by bending analuminum pipe having no welded seams, a plurality of first plate fins 5of aluminum each having two holes 5 a spaced apart in the forward orrearward direction, and aluminum plate fins 11 each having two holes 11a spaced apart in the forward or rearward direction (see FIG. 5).

The hairpin tube 10 is integrally provided with high and low two kindsof inner fins 20, 21 projecting from the inner peripheral surface of thetube to different heights, extending longitudinally thereof, andalternately arranged circumferentially thereof at a spacing. The innerfins 20, 21 are the same as those already described with reference toFIG. 2.

As shown in FIG. 5, the plate fins 5, 11 are rectangular and elongatedin the forward or rearward direction. The plate fin 11 has a V-shapednotch 12 formed in the midportion of each of upper and lower edgesthereof along the forward or rearward direction, and a slit 13 extendingbetween the notches 12 widthwise (upward or downward) of the plate fin11. The holes 11 a are positioned respectively on the front and rearsides of the slit 13. The distance between each end of the slit 13 andthe notch 12 is preferably about 0.1 to about 0.4 mm. The plate fin 11having the notches 12 and the slit 13 will hereinafter be referred to asthe “slitted plate fin.” The slitted plate fin 11 is formed by blankingwith a die which is used for blanking out the first plate fin 5 andwhich has notch forming portions and a slit forming portion removablyattached thereto. With the notches 12 and the slit 13 formed, theslitted plate fin 11 comprises front and rear two fin forming portions15 and connecting portions 16 each positioned between the notch 12 andthe slit 13 and joining the two fin forming portions 15 dividably.

The two straight tube portions 10 a of the hairpin tube 10 are theninserted through the respective holes 5 a, 11 a of all plate fins 5, 11to thereby provide a plurality of, i.e. in this case, four, unfixed fingroups arranged on the straight tube portions 2 a at a spacinglongitudinally thereof and each comprising plate fins 5 or 11. The twounfixed fin groups toward the bent portion 10 b of the hairpin tube 10each comprise first plate fins 5 and provide the first fin groups 3 ofthe finned zigzag tube 1. The two unfixed fin groups toward the two endopenings of the hairpin tube 20 each comprise slitted plate fins 11 andprovide the second fin groups 4 of the finned zigzag tube 1. The spacingbetween the unfixed fin groups providing the first fin groups 3 is alength permitting the two straight tubes 10 a to be so bent as toposition the first fin groups 3 one above the other in superposedlayers, and is equal to the spacing between the unfixed fin groupsproviding the second fin groups 4. The total number of unfixed fingroups is n (which is an integer of not smaller than 2) times the numberof unfixed fin groups providing the first fin groups 4.

A pressure fluid such as water, oil or air is then introduced into thehairpin tube 10 in this state to enlarge the tube to fixedly fit thefirst plate fins 5 and the slitted plate fins 11 of the unfixed fingroups around the two straight tube portions 10 a of the hairpin tube 10and to thereby fabricate a finned hairpin tube H which has two dividablefin groups 14 providing the second fin groups 4, and two first fingroups 3 (see FIG. 4). The hairpin tube 10 may be enlarged alternativelyby preparing a tube enlarging device comprising a pressure rod and atube enlarging mandrel attached to the forward end of the rod andforcing the mandrel of the device into the straight tube portions 2 afrom end openings of the hairpin tube 10.

The finned hairpin tube H is thereafter made into a finned zigzag tube1. First, the slitted plate fins 11 constituting the two dividable fingroups 14 of the hairpin tube 10 are divided at the connecting portions16 between the slit 13 and the notches 12 into portions fixed to one ofthe straight tube portions 10 a and the portions fixed to the otherstraight tube portion 10 a to form second fin groups 4. Each slittedplate fin 11 is divided by pulling the fin 11 apart forward andrearward, with a wedge pressed against the two notches 12. Subsequently,the two straight tube portions 10 a of hairpin tube 10 of the finnedhairpin tube H are bent outward between the first fin group 3, i.e., thesecond as counted from the bent portion of the tube 10, and the secondfin group 4, i.e., the third as counted from the bent portion, forwardlyand rearwardly respectively (see chain lines in FIG. 1). In this way, afinned zigzag tube 1 is fabricated which comprises a plurality of firstfin groups 3 arranged at a spacing on the two adjacent straight tubeportions 2 a in the center of the zigzag tube 2 longitudinally of theportions 2 a, and a plurality of second fin groups 4 arranged at aspacing on the respective straight tube portions 2 a at the front andrear ends of the zigzag tube 2 longitudinally of the portions 2 a.

Finally, the finned zigzag tube 1 is bent at a location between theadjacent first fin groups 3 and between the second fin groups 4 whereall the straight tube portions 2 a are arranged, so as to position thefirst fin groups 3 one above the other and the second fin groups 4 oneabove the other in superposed layers, whereby an evaporator E isfabricated (see chain lines in FIG. 3).

The evaporator E has a refrigeration cycle having a compressor, acondenser and an evaporator, and is used as an evaporator inrefrigeration devices, such as refrigerators or refrigerated showcases,wherein a hydrocarbon refrigerant is used as the refrigerant andcirculated at a rate as low as 1 to 9 kg/h.

With the foregoing embodiment, the zigzag tube 2 constituting the finnedzigzag tube 1 for making the evaporator E has straight tube portions 2 awhich are 4 in number, and the dividable fin groups 14 comprisingslitted plate fins 11 and included in the finned hairpin tube H aretherefore equal to the first fin groups 3 in number. However, the numberof straight tube portions 2 a is not limitative but can be any numberrepresented by 2n (wherein n is an integer of not smaller than 2). Inthis case, the number of dividable fin groups 14 comprising slittedplate fins 11 and included in the finned hairpin tube H is made equal to(n−1) times the number of first fin groups 3. A finned zigzag tube isthen formed by bending zigzag the two straight tube portions 10 a ofhairpin tube 10 of the finned hairpin tube H forwardly and rearwardlyoutward. Although there arises a case wherein the number of straighttube portions 2 a of zigzag tube 2 constituting the finned zigzag tube 1is an odd number of at least 3, i.e., 2n−1 (wherein n is an integer ofnot smaller than 2), this case can then be handled by dividing theslitted plate fins 11 of the dividable fin groups 14 and cutting off oneof the straight tube portions 10 a of the hairpin tube 10 over a lengthfrom the end opening thereof which length has second fin groups 4 whichare equal in number to the number of first fin groups 3.

According to the embodiment described above, the first fin groups 3 andthe second fin groups 4 of the evaporator are arranged in two superposedlayers, whereas this arrangement is not limitative but these fin groupsmay be arranged in at least three superposed layers. The finned zigzagtube 1 are then at least three in the number of first fin groups 3, aswell as of second fin groups 4. The first fin groups 3 and second fingroups 4 may be provided in only one layer. In this case, the fin groups3 and 4 may each be only one in number.

Further according to the foregoing and other embodiments, the plate finsto be divided need not always have the slit 13 or notch 12.

The heat exchanger of the invention is usable also as means other thanthe evaporator of the refrigerant device.

FIG. 6 shows a modification of zigzag tube 2 constituting a finnedzigzag tube 1 for use in fabricating evaporators.

With reference to FIG. 6, the illustrated zigzag tube 2 is integrallyprovided with a plurality of inner fins 22 projecting from the innerperipheral surface of the tube to equal heights, extendinglongitudinally thereof, and arranged circumferentially thereof at aspacing. The inner fins 22 are 0.7 to 1.2 mm in height h3 as measuredfrom the inner peripheral surface of the zigzag tube 2. The inner fins22 are 0.4 to 1.6 mm in pitch p. The term “pitch p” of the inner fins 22has the same meaning as already described. The zigzag tube 2 is 6 to 10mm in outside diameter, and 0.4 to 0.8 mm in the thickness of thecircumferential wall thereof.

INDUSTRIAL APPLICABILITY

The heat exchanger of the present invention is useful as an evaporatorfor refrigeration devices, such as refrigerators or refrigeratedshowcases, and is especially suitable for use as an evaporator inrefrigeration devices wherein a hydrocarbon refrigerant is used.

1. A heat exchanger comprising a zigzag tube formed by bending a pipe having no welded seams and having at least three straight tube portions arranged from the front rearward at a spacing and parallel to one another, and a plurality of plate fins fixedly fitted around the straight tube portions.
 2. A heat exchanger according to claim 1 which comprises a first fin group comprising a plurality of plate fins extending across and fixedly arranged in parallel on two adjacent straight tube portions of the zigzag tube, and a second fin group comprising a plurality of plate fins fixedly arranged in parallel on each remaining straight tube portion of the zigzag tube.
 3. A heat exchanger according to claim 1 wherein the zigzag tube is integrally provided on an inner peripheral surface thereof with inner fins extending longitudinally thereof and arranged at a spacing circumferentially thereof.
 4. A heat exchanger according to claim 3 wherein each of the plate fins is fixed to the straight tube portion of the zigzag tube by enlarging the tube with use of a fluid.
 5. A the heat exchanger according to claim 3 wherein the zigzag tube has high and low two kinds of inner fins alternately arranged circumferentially thereof and projecting from the inner peripheral surface of the tube to different heights, the high inner fins being 0.7 to 1.7 mm in height from the tube surface, the low inner fins being 0.4 to 1.2 mm in height from the surface.
 6. A heat exchanger according to claim 5 wherein the pitch of the inner fins is 0.4 to 1.6 mm.
 7. A heat exchanger according to claim 5 wherein the zigzag tube is 6 to 10 mm in outside diameter and 0.4 to 0.8 mm in the wall thickness of a circumferential wall thereof.
 8. A heat exchanger according to claim 3 wherein all the inner fins are equal in height and are 0.7 to 1.2 mm in height from the inner peripheral surface of the zigzag tube.
 9. A heat exchanger according to claim 8 wherein the pitch of the inner fins is 0.4 to 1.6 mm.
 10. A heat exchanger according to claim 8 wherein the zigzag tube is 6 to 10 mm in outside diameter and 0.4 to 0.8 mm in the wall thickness of a circumferential wall thereof.
 11. A heat exchanger according to claim 2 wherein the front-to-rear length of the plate fins of the second fin group is approximately one half the front-to-rear length of the plate fins of the first fin group.
 12. A heat exchanger according to claim 2 wherein the first fin group is different from the second fin group in fin pitch.
 13. A heat exchanger according to claim 12 wherein the second fin group is greater than the first fin group in fin pitch.
 14. A heat exchanger comprising a finned zigzag tube including a zigzag tube member formed by bending a pipe having no welded seams, the zigzag tube member having at least three straight tube portions arranged from the front rearward at a spacing and parallel to one another, a plurality of first fin groups arranged at a spacing on two adjacent straight tube portions of the zigzag tube member longitudinally of the straight tube portions and each comprising a plurality of plate fins extending across and fixedly arranged in parallel on the adjacent straight tube portions, and a plurality of second fin groups each comprising a plurality of plate fins fixedly arranged in parallel on each remaining straight tube portion of the zigzag tube member, the second fin groups being arranged at a spacing on the remaining straight tube portion longitudinally thereof so as to be in the same positions as the respective first fin groups with respect to the longitudinally direction of the straight tube portions, the finned zigzag tube being bent between the first fin groups and between the second fin groups on all the straight tube portions so as to position the first fin groups one above another and the second fin groups one above another in superposed layers, the spacing between the adjacent first fin groups and the spacing between the second fin groups being a length permitting bending of the straight tube portions of the finned zigzag tube.
 15. A heat exchanger according to claim 14 wherein the zigzag tube member is integrally provided on an inner peripheral surface thereof with inner fins extending longitudinally thereof and arranged at a spacing circumferentially thereof.
 16. A heat exchanger according to claim 15 wherein each of the plate fins is fixed to the straight tube portion of the zigzag tube member by enlarging the tube member with use of a fluid.
 17. A heat exchanger according to claim 15 wherein the zigzag tube member has high and low two kinds of inner fins alternately arranged circumferentially thereof and projecting from the inner peripheral surface of the tube member to different heights, the high inner fins being 0.7 to 1.7 mm in height from the tube member surface, the low inner fins being 0.4 to 1.2 mm in height from the surface.
 18. A heat exchanger according to claim 17 wherein the pitch of the inner fins is 0.4 to 1.6 mm.
 19. A heat exchanger according to claim 17 wherein the zigzag tube member is 6 to 10 mm in outside diameter and 0.4 to 0.8 mm in the wall thickness of a circumferential wall thereof.
 20. A heat exchanger according to claim 15 wherein all the inner fins are equal in height and are 0.7 to 1.2 mm in height from the inner peripheral surface of the zigzag tube member.
 21. A heat exchanger according to claim 20 wherein the pitch of the inner fins is 0.4 to 1.6 mm.
 22. A heat exchanger according to claim 20 wherein the zigzag tube member is 6 to 10 mm in outside diameter and 0.4 to 0.8 mm in the wall thickness of a circumferential wall thereof.
 23. A heat exchanger according to claim 14 wherein the front-to-rear length of the plate fins of the second fin groups is approximately one half the front-to-rear length of the plate fins of the first fin groups.
 24. A heat exchanger according to claim 14 wherein the first fin groups is different from the second fin groups in fin pitch.
 25. A heat exchanger according to claim 24 wherein the second fin groups are greater than the first fin groups in fin pitch.
 26. A refrigeration device which has a refrigeration cycle having a compressor, a condenser and an evaporator, the evaporator comprising a heat exchanger according to claim 1 wherein a hydrocarbon refrigerant is used as the refrigerant and circulated at a rate of 1 to 9 kg/h.
 27. A process for fabricating a heat exchanger according to claim 2, which process includes preparing a hairpin tube by bending a pipe having no welded seams and a multiplicity of plate fins each having two holes spaced apart from the front rearward, inserting two straight tube portions of the hairpin tube through the respective holes of all the plate fins to thereby arrange the plate fins in parallel into a predetermined number of unfixed fin groups spaced apart on the straight tube portions longitudinally thereof by a length permitting bending of the straight tube portions; enlarging the hairpin tube to fixedly position the plate fins across the two straight tube portions to obtain a finned hairpin tube having a dividable fin group for forming second fin groups and a first fin group; dividing the plate fins of the entire dividable fin group into portions fixed to one of the straight tube portions and portions fixed to the other straight tube portion to form the second fin groups and outwardly bending the two straight tube portions of the finned hairpin tube forward and rearward respectively.
 28. A process for fabricating a heat exchanger according to claim 14, which process includes preparing a hairpin tube by bending a pipe having no welded seams and a multiplicity of plate fins each having two holes spaced apart in a forward or rearward direction, inserting two straight tube portions of the hairpin tube through the respective holes of all the plate fins to thereby arrange the plate fins in parallel into a predetermined number of unfixed fin groups spaced apart on the straight tube portions longitudinally thereof by a length permitting bending of the straight tube portions; the predetermined number being n (which is an integer of not smaller than 2) times the number, not smaller than 2, of unfixed fin groups positioned closer to a bent portion of the hairpin tube for forming first fin groups; enlarging the hairpin tube to fixedly position the plate fins across the two straight tube portions to obtain a finned hairpin tube having dividable fin groups for forming second fin groups and the first fin group; dividing the plate fins of all the dividable fin groups into portions fixed to one of the straight tube portions and portions fixed to the other straight tube portion to form the second fin groups and outwardly bending the two straight tube portions of the finned hairpin tube forward and rearward respectively.
 29. A process for fabricating a heat exchanger according to claim 27 wherein the hairpin tube is integrally provided on an inner peripheral surface thereof with inner fins extending longitudinally thereof and arranged at a spacing circumferentially thereof.
 30. A process for fabricating a heat exchanger according to claim 27 wherein the hairpin tube is enlarged with use of a fluid.
 31. A process for fabricating a heat exchanger according to claim 29 wherein the hairpin tube has high and low two kinds of inner fins alternately arranged circumferentially thereof and projecting from the inner peripheral surface of the tube to different heights, the high inner fins being 0.7 to 1.7 mm in height from the tube surface, the low inner fins being 0.4 to 1.2 mm in height from the surface.
 32. A process for fabricating a heat exchanger according to claim 31 wherein the pitch of the inner fins is 0.4 to 1.6 mm.
 33. A process for fabricating a heat exchanger according to claim 31 wherein the hairpin tube is 6 to 10 mm in outside diameter and 0.4 to 0.8 mm in the wall thickness of a circumferential wall thereof.
 34. A process for fabricating a heat exchanger according to claim 29 wherein all the inner fins are equal in height and are 0.7 to 1.2 mm in height from the inner peripheral surface of the hairpin tube.
 35. A process for fabricating a heat exchanger according to claim 34 wherein the pitch of the inner fins is 0.4 to 1.6 mm.
 36. A process for fabricating a heat exchanger according to claim 34 wherein the hairpin tube is 6 to 10 mm in outside diameter and 0.4 to 0.8 mm in the wall thickness of a circumferential wall thereof.
 37. A process for fabricating a heat exchanger according to claim 27 wherein the plate fins of the dividable fin group for forming the second fin groups each comprise two fin forming portions and connecting portions dividably joining the two fin forming portions.
 38. A process for fabricating a heat exchanger according to claim 27 wherein the plate fins of the first fin group and the plate fins of the dividable fin group for forming the second fin groups are identical in shape, and the plate fins of the dividable fin group each have a V-shaped notch formed in a midportion of at least one of upper and lower edges thereof in the forward or rearward direction, and a slit extending upward or downward and formed at the same position as the notch with respect to the forward or rearward direction, as separated from the notch.
 39. A process for fabricating a heat exchanger according to claim 27 wherein a straight tube portion having a predetermined number of second fin groups is cut off from the finned hairpin tube after the second fin groups are formed by dividing the dividable fin group. 